Vascular dementia
Vascular dementia is caused when there is an interruption in the blood supply to the brain.
Like all organs, in order to work properly, the brain needs a constant supply of oxygen and nutrients, which is provided by your blood (vascular system). If the supply of blood is restricted or stopped, brain cells begin to die, resulting in brain damage.
This interruption to blood supply can develop gradually over time if the vessels inside the brain narrow and harden. This narrowing and hardening of the blood vessels is usually caused when fatty deposits build up on the blood vessel walls, restricting the flow of blood. This is called atherosclerosis.
Known risk factors for atherosclerosis include:
- diabetes
- obesity
- smoking
- drinking too much alcohol
- lack of exercise
- eating a high-fat diet
Atherosclerosis in the smaller blood vessels in the brain will also cause them to gradually clog up, depriving the brain of blood. This is known as small vessel disease.
The blood supply to the brain is interrupted rapidly during a stroke and this can also cause damage to the brain cells.
Not everyone who has had a stroke will go on to have vascular dementia. However, if you have had a stroke or have been diagnosed with small vessel disease, you may be at higher risk of developing vascular dementia.
Dementia with Lewy bodies
Lewy bodies are small, circular lumps of protein that develop inside the brain. It is not known what causes them. It is also unclear how they damage the brain and cause dementia. One theory is that they block the effects of two neurotransmitters called dopamine and acetylcholine.
Neurotransmitters are messenger chemicals that send information from one brain cell to another.
Both dopamine and acetylcholine are thought to play an important role in helping to regulate many brain functions, such as memory, learning, mood and attention. Therefore, by blocking their effects, Lewy bodies may trigger dementia.
Fronto-temporal dementia
Fronto-temporal dementia is caused by two parts of the brain (the temporal lobe and the frontal lobe) becoming increasingly damaged and then shrinking.
In an estimated 40-50% of cases, people who develop fronto-temporal dementia have inherited a genetic mutation (an altered gene) from their parents. These genetic mutations are thought to have a negative effect on a protein called the tau protein.
All brain cells contain tau proteins that help to keep them stable. However, if tau proteins stop working properly, they can damage brain cells.
Motor neurone disease is also known to cause fronto-temporal dementia.
Less common causes of dementia
Dementia or dementia-like symptoms can have a number of less common causes, some of which are treatable. These include:
- repeated injury to the head
- infections of the brain, such as meningitis or encephalitis
- Huntington's disease, a rare genetic condition that causes progressive brain damage
- Creutzfeldt-Jakob disease (CJD), a rare and fatal condition that causes damage to the brain and nervous system
- an overactive or underactive thyroid gland
- dehydration
- lack of vitamin B in the diet
- poisoning, for example from lead or pesticides
- having a brain tumour
- certain lung and heart conditions that interrupt the supply of blood and oxygen to the brain
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